1. Technical Field
The present invention relates to a technique using a plasma for repairing a decarbonized, damaged layer in a film having a low dielectric constant (hereinafter referred to as “low-dielectric-constant film”) and containing silicon, carbon, oxygen and hydrogen.
2. Description of the Related Art
There is a growing tendency for the scale of integration of semiconductor devices to increase every year. Resists and exposure techniques have been progressively improved to deal with the progressive miniaturization of patterns formed on a substrate, such as a semiconductor wafer (hereinafter, referred to simply as “wafer”), and the dimensions of apertures formed in resist masks have been remarkably decreased.
On the other hand, multiple-layer devices have been developed to achieve increasing the scale of integration. The parasitic capacitances of the semiconductor device need to be reduced to improve the circuit speed. Therefore, efforts have been made to develop materials having a low dielectric constant for forming insulating films, such as layer insulating films. An example of such a desirable insulating film is SiOCH film generally called a porous MSQ film having Si—C bonds (Methyl-hydrogen-silses-quioxane film).
The SiOCH film, in which copper lines or such are embedded, is etched with a CF4 plasma produced by ionizing CF4 gas through a resist mask and a hard mask, and the resist mask is removed by an ashing process using an oxygen plasma produced by ionizing oxygen gas. FIG. 14 is a typical view illustrating processing the SiOC film. Shown in FIG. 14 are a SiOCH film, a resist mask 101 and a hard mask 102.
When the SiOCH film 100 is subjected to a plasma-etching process or a plasma-ashing process, Si—C bonds in a surface layer exposed to a plasma in the SiOCH film formed on the side walls and the bottom wall of a recess are broken and C atoms are eliminated from the SiOCH film and Si atoms having dangling bonds remains in the surface layer. Si atoms having dangling bonds formed through elimination of C atoms from Si—C bonds are unstable. The unstable Si atoms and moisture contained in the atmosphere bond together to produce Si—OH bonds.
Thus the plasma etching process or the plasma ashing process damages the exposed surface layer of the SiOCH film and forms a damaged layer 103. Since the damaged layer 103 has a low carbon content and hence has a low dielectric constant. The width of lines forming a wiring pattern and the thickness of wiring layers and insulating films have been progressively reduced. Therefore, the significance of the influence of the surface layer relative to that of a wafer W has increased and even the reduction of the dielectric constant of the surface layer can be one of factors that cause the characteristics of a semiconductor device to differ from design characteristics.
A method of solving such a problem is disclosed in JP-A 2005-340288 (Paragraphs [0010] and [0028]). This previously proposed method modifies the damaged surface layer containing OH groups produced by dry etching by using a silazane compound having Si—Si bonds and Si—CH3 bonds. This method is a surface modification method that replaces the hydrogen atoms of the OH groups with the silazane compound and does not restore the damage surface layer to its original state before the plasma etching process or the plasma ashing process. Therefore the dielectric constant of the SiOCH film is different from a design dielectric constant. Since the molecules of the silazane compound are large, molecules formed by replacing the hydrogen atoms of the OH groups with the silazane compound cause steric hindrance, molecules cannot penetrate deep into the film and hence the interior of the film cannot be modified.